Method and apparatus for reducing signaling overhead in a wireless communication network

ABSTRACT

A method and apparatus are disclosed for reducing signaling overhead in a wireless communication network. In one embodiment, the method is implemented in a UE. The method includes receiving a first indication from a network node to tell the UE to remember, after the UE enters RRC_IDLE, a first configuration which is currently used while the UE is in RRC_CONNECTED. The method also includes keeping the first configuration upon leaving RRC_CONNECTED. The method further includes releasing the first configuration when the UE connects to a RAT different from where the first indication was received.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a continuation of U.S. patent application Ser. No.13/941,974, filed Jul. 15, 2013, which claims the benefit of U.S.Provisional Patent Application Ser. No. 61/672,429, filed on Jul. 17,2012, the entire disclosure of which is incorporated herein byreference.

FIELD

This disclosure generally relates to wireless communication networks,and more particularly, to a method and apparatus for reducing signalingoverhead in a wireless communication network.

BACKGROUND

With the rapid rise in demand for communication of large amounts of datato and from mobile communication devices, traditional mobile voicecommunication networks are evolving into networks that communicate withInternet Protocol (IP) data packets. Such IP data packet communicationcan provide users of mobile communication devices with voice over IP,multimedia, multicast and on-demand communication services.

An exemplary network structure for which standardization is currentlytaking place is an Evolved Universal Terrestrial Radio Access Network(E-UTRAN). The E-UTRAN system can provide high data throughput in orderto realize the above-noted voice over IP and multimedia services. TheE-UTRAN system's standardization work is currently being performed bythe 3GPP standards organization. Accordingly, changes to the currentbody of 3GPP standard are currently being submitted and considered toevolve and finalize the 3GPP standard.

SUMMARY

A method and apparatus are disclosed for reducing signaling overhead ina wireless communication network. In one embodiment, the method isimplemented in a UE (User Equipment). The method includes receiving afirst indication from a network node to tell the UE to remember, afterthe UE enters RRC_IDLE, a first configuration which is currently usedwhile the UE is in RRC_CONNECTED. The method also includes keeping thefirst configuration upon leaving RRC_CONNECTED. The method furtherincludes releasing the first configuration when the UE connects to aRadio Access Technology (RAT) different from where the first indicationwas received.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 shows a diagram of a wireless communication system according toone exemplary embodiment.

FIG. 2 is a block diagram of a transmitter system (also known as accessnetwork) and a receiver system (also known as user equipment or UE)according to one exemplary embodiment.

FIG. 3 is a functional block diagram of a communication system accordingto one exemplary embodiment.

FIG. 4 is a functional block diagram of the program code of FIG. 3according to one exemplary embodiment.

FIG. 5 is a histogram illustrating traffic amount for different devicesaccording to one exemplary embodiment.

FIG. 6 is a message sequence chart of a RRC (Radio Resource Control)procedure according to one exemplary embodiment.

FIGS. 7, 8 and 9 are flow charts according to exemplary embodiments.

DETAILED DESCRIPTION

The exemplary wireless communication systems and devices described belowemploy a wireless communication system, supporting a broadcast service.Wireless communication systems are widely deployed to provide varioustypes of communication such as voice, data, and so on. These systems maybe based on code division multiple access (CDMA), time division multipleaccess (TDMA), orthogonal frequency division multiple access (OFDMA),3GPP LTE (Long Term Evolution) wireless access, 3GPP LTE-A orLTE-Advanced (Long Term Evolution Advanced), 3GPP2 UMB (Ultra MobileBroadband), WiMax, or some other modulation techniques.

In particular, the exemplary wireless communication systems devicesdescribed below may be designed to support one or more standards such asthe standard offered by a consortium named “3rd Generation PartnershipProject” referred to herein as 3GPP, including Document Nos. RWS-120050,“LG's view on evolution of LTE in Release 12 and beyond”, LG;RWS-120014, “Towards LTE RAN Evolution”, Alcatel-Lucent; RWS-120003,“Views on Rel-12”, Ericsson; RWS-120006, “Views on Rel-12 and onwardsfor LTE and UMTS”, Huawei; RWS-120011, “Where to improve Rel-12 andbeyond: Promising technologies”, NEC; TS 36.331 V11.0.0, “E-UTRA RRCprotocol specification (Release 11)”; and 3GPP TS 33.401 V11.4.0, “3GPPSystem Architecture Evolution (SAE); Security architecture”. Thestandards and documents listed above are hereby expressly incorporatedherein.

FIG. 1 shows a multiple access wireless communication system accordingto one embodiment of the invention. An access network 100 (AN) includesmultiple antenna groups, one including 104 and 106, another including108 and 110, and an additional including 112 and 114. In FIG. 1, onlytwo antennas are shown for each antenna group, however, more or fewerantennas may be utilized for each antenna group. Access terminal 116(AT) is in communication with antennas 112 and 114, where antennas 112and 114 transmit information to access terminal 116 over forward link120 and receive information from access terminal 116 over reverse link118. Access terminal (AT) 122 is in communication with antennas 106 and108, where antennas 106 and 108 transmit information to access terminal(AT) 122 over forward link 126 and receive information from accessterminal (AT) 122 over reverse link 124. In a FDD system, communicationlinks 118, 120, 124 and 126 may use different frequency forcommunication. For example, forward link 120 may use a differentfrequency then that used by reverse link 118.

Each group of antennas and/or the area in which they are designed tocommunicate is often referred to as a sector of the access network. Inthe embodiment, antenna groups each are designed to communicate toaccess terminals in a sector of the areas covered by access network 100.

In communication over forward links 120 and 126, the transmittingantennas of access network 100 may utilize beamforming in order toimprove the signal-to-noise ratio of forward links for the differentaccess terminals 116 and 122. Also, an access network using beamformingto transmit to access terminals scattered randomly through its coveragecauses less interference to access terminals in neighboring cells thanan access network transmitting through a single antenna to all itsaccess terminals.

An access network (AN) may be a fixed station or base station used forcommunicating with the terminals and may also be referred to as anaccess point, a Node B, a base station, an enhanced base station, aneNodeB, or some other terminology. An access terminal (AT) may also becalled user equipment (UE), a wireless communication device, terminal,access terminal or some other terminology.

FIG. 2 is a simplified block diagram of an embodiment of a transmittersystem 210 (also known as the access network) and a receiver system 250(also known as access terminal (AT) or user equipment (UE)) in a MIMOsystem 200. At the transmitter system 210, traffic data for a number ofdata streams is provided from a data source 212 to a transmit (TX) dataprocessor 214.

In one embodiment, each data stream is transmitted over a respectivetransmit antenna. TX data processor 214 formats, codes, and interleavesthe traffic data for each data stream based on a particular codingscheme selected for that data stream to provide coded data.

The coded data for each data stream may be multiplexed with pilot datausing OFDM techniques. The pilot data is typically a known data patternthat is processed in a known manner and may be used at the receiversystem to estimate the channel response. The multiplexed pilot and codeddata for each data stream is then modulated (i.e., symbol mapped) basedon a particular modulation scheme (e.g., BPSK, QPSK, M-PSK, or M-QAM)selected for that data stream to provide modulation symbols. The datarate, coding, and modulation for each data stream may be determined byinstructions performed by processor 230.

The modulation symbols for all data streams are then provided to a TXMIMO processor 220, which may further process the modulation symbols(e.g., for OFDM). TX MIMO processor 220 then provides N_(T) modulationsymbol streams to N_(T) transmitters (TMTR) 222 a through 222 t. Incertain embodiments, TX MIMO processor 220 applies beamforming weightsto the symbols of the data streams and to the antenna from which thesymbol is being transmitted.

Each transmitter 222 receives and processes a respective symbol streamto provide one or more analog signals, and further conditions (e.g.,amplifies, filters, and upconverts) the analog signals to provide amodulated signal suitable for transmission over the MIMO channel. N_(T)modulated signals from transmitters 222 a through 222 t are thentransmitted from N_(T) antennas 224 a through 224 t, respectively.

At receiver system 250, the transmitted modulated signals are receivedby N_(R) antennas 252 a through 252 r and the received signal from eachantenna 252 is provided to a respective receiver (RCVR) 254 a through254 r. Each receiver 254 conditions (e.g., filters, amplifies, anddownconverts) a respective received signal, digitizes the conditionedsignal to provide samples, and further processes the samples to providea corresponding “received” symbol stream.

An RX data processor 260 then receives and processes the N_(R) receivedsymbol streams from N_(R) receivers 254 based on a particular receiverprocessing technique to provide N_(T) “detected” symbol streams. The RXdata processor 260 then demodulates, deinterleaves, and decodes eachdetected symbol stream to recover the traffic data for the data stream.The processing by RX data processor 260 is complementary to thatperformed by TX MIMO processor 220 and TX data processor 214 attransmitter system 210.

A processor 270 periodically determines which pre-coding matrix to use(discussed below). Processor 270 formulates a reverse link messagecomprising a matrix index portion and a rank value portion.

The reverse link message may comprise various types of informationregarding the communication link and/or the received data stream. Thereverse link message is then processed by a TX data processor 238, whichalso receives traffic data for a number of data streams from a datasource 236, modulated by a modulator 280, conditioned by transmitters254 a through 254 r, and transmitted back to transmitter system 210.

At transmitter system 210, the modulated signals from receiver system250 are received by antennas 224, conditioned by receivers 222,demodulated by a demodulator 240, and processed by a RX data processor242 to extract the reserve link message transmitted by the receiversystem 250. Processor 230 then determines which pre-coding matrix to usefor determining the beamforming weights then processes the extractedmessage.

Turning to FIG. 3, this figure shows an alternative simplifiedfunctional block diagram of a communication device according to oneembodiment of the invention. As shown in FIG. 3, the communicationdevice 300 in a wireless communication system can be utilized forrealizing the UEs (or ATs) 116 and 122 in FIG. 1, and the wirelesscommunications system is preferably the LTE system. The communicationdevice 300 may include an input device 302, an output device 304, acontrol circuit 306, a central processing unit (CPU) 308, a memory 310,a program code 312, and a transceiver 314. The control circuit 306executes the program code 312 in the memory 310 through the CPU 308,thereby controlling an operation of the communications device 300. Thecommunications device 300 can receive signals input by a user throughthe input device 302, such as a keyboard or keypad, and can outputimages and sounds through the output device 304, such as a monitor orspeakers. The transceiver 314 is used to receive and transmit wirelesssignals, delivering received signals to the control circuit 306, andoutputting signals generated by the control circuit 306 wirelessly.

FIG. 4 is a simplified block diagram of the program code 312 shown inFIG. 3 in accordance with one embodiment of the invention. In thisembodiment, the program code 312 includes an application layer 400, aLayer 3 portion 402, and a Layer 2 portion 404, and is coupled to aLayer 1 portion 406. The Layer 3 portion 402 generally performs radioresource control. The Layer 2 portion 404 generally performs linkcontrol. The Layer 1 portion 406 generally performs physicalconnections.

FIG. 5 is a histogram 500 illustrating traffic amount for differencedevices in accordance with one exemplary embodiment. The histogram 500can be found in 3GPP RWS-120050. As illustrated in to FIG. 5, the numberof devices and traffic amount per device grows virtually exponentiallyevery year. Furthermore, it is pointed out in 3GPP RWS-120014 that in2020, there would be 20 billion M2M devices where 500% M2M (Machine ToMachine) traffic would be increased and 83% of M2M revenue would begenerated from value-added services. In addition, as discussed in 3GPPRWS-120003, it is expected that in the future, there would be a widerange of applications with very different requirements using machinetype communication (MTC), such as consumer electronics, smart grid,surveillance, epayment, security, smart transportation, etc. Thus, it ismentioned that the following aspects are important to improve MTC:

-   -   Low-cost devices    -   Reduced power consumption    -   Signaling load reductions

Furthermore, 3GPP RWS-120006 proposes several MTC optimizations forRel-12 as follows:

-   -   Efficient support of large amount of MTC devices with small data        transmission    -   RRC signaling reduction    -   Efficient physical layer resource usage (e.g. PDCCH/PUCCH/SRS)    -   Low power consumption for MTC devices    -   Co-work with SA2 for MTC enhancements

In addition, as considered and discussed in 3GPP RWS-120011, diversedata applications (DDA) have similar problems as MTC as follows:

-   -   In Rel-10 and Rel-11, enhancements for MTC and diverse data        applications have been introduced. Traffic/congestion management        based on application types is studied for Rel-12.    -   However, RRC in RAN is still inefficient in terms of management        overhead for applications with in-frequent, small-volume packet        traffic.

Therefore, 3GPP RWS-120011 proposes the following optimizations for bothMTC and DDA:

-   -   Reduced state and control plane overhead    -   Lower energy consumption    -   Better support for diverse data application

As seen, one consensus of different documents is to improve MTC or DDAis to reduce signaling overhead. One possible alternative to reducesignaling overhead is to keep all UEs, which runs MTC or DDA forexample, in RRC_CONNECTED to reduce signaling used for transitionbetween RRC_IDLE and RRC_CONNECTED. However, due to the increasingnumber of devices year by year, keeping all UEs in RRC_CONNECTED may notbe easily achieved in the future because of insufficient capacity orresources. Thus other alternatives to reduce signaling overhead shouldalso be considered.

As discussed in the current RRC specification (3GPP TS 36.331 V11.0.0),every time when a UE enters RRC_CONNECTED from RRC_IDLE to transmit userplane data, three procedures (including RRC connection establishment,security mode command, and RRC connection reconfiguration) are requiredto be performed following the order shown in FIG. 6:

-   -   Steps 1-3: In general, the purpose of this procedure is to        establish an RRC connection. RRC connection establishment        involves SRB1 establishment. The procedure is also used to        transfer the initial NAS dedicated information/message from the        UE to E-UTRAN.    -   Steps 4-5: In general, the purpose of this procedure is to        activate AS security upon RRC connection establishment.    -   Steps 6-7: In general, the purpose of this procedure is to        modify an RRC connection, such as to establish/modify/release        RBs, to perform handover, to setup/modify/release measurements,        to add/modify/release SCells. As part of the procedure, NAS        dedicated information may be transferred from E-UTRAN to the UE.

For some types of MTC devices or for some specific types of dataapplications, a UE performs state transition from an idle state to aconnected state just for the purpose of transmitting a small amount ofdata. In such cases, the amount of signaling caused by the RRCprocedures is quite significant compared with the amount of thetransmitted user data. If the RRC procedures required for transitionfrom RRC_IDLE to RRC_CONNECTED could be simplified, the signalingoverhead could be reduced.

For a stationary or low mobility UE running MTC or DDA, the radiocondition, required resources, and/or on-going applications may not bechanged frequently. As a result, when the UE enters RRC_CONNECTED totransmit data, the required RB (Radio Bearer) configuration for SRB(Signaling Radio Bearer) and/or DRB (Data Radio Bearer), MAC (MediumAccess Control) configuration, physical channel configuration, and/ormeasurement configuration may be quite similar or (partially) the same.

Based on above, the general concept of the invention is to re-use theconfiguration during last time a UE in RRC_CONNECTED so that theprevious configuration could be used as the basis for delta signaling,or the whole procedure could be omitted.

If the UE's previous configuration (which was applied during last timethe UE in RRC_CONNECTED) could be reused, the configuration would notneed to be signaled, and thus the signaling overhead of the RRCconnection reconfiguration procedure could be reduced (for example, bytreating the configuration applied during last time as the basis fordelta signaling, or by even omitting the entire RRC connectionreconfiguration procedure). Furthermore, if security key(s), such asK_(eNB) described in 3GPP TS 33.401 V11.4.0, and/or securityalgorithm(s) of a UE applied during last time the UE in RRC_CONNECTEDcould be reused, signaling overhead of the security mode commandprocedure could be reduced or omitted altogether. As a result, signalingoverhead could be reduced by reusing previous configuration when aspecific UE enters RRC_CONNECTED from RRC_IDLE and by omitting thesecurity procedure and/or RRC connection reconfiguration procedure.

One concern may be how to synchronize UE configuration between the UEand network or eNB. Currently, as discussed in 3GPP TS 36.331 V11.0.0,S-TMSI (System Architecture Evolution Temporary Mobile StationIdentifier) is included in the RRCConnectionRequest message if the UE isregistered in the TA of the current cell. The eNB could store theprevious UE configuration and could identify the UE by the S-TMSI. As aresult, there would be no configuration synchronization problem.

FIG. 7 is a flow chart 700 in accordance with an exemplary embodiment.In step 705 of FIG. 7, an indication is used to tell a UE whether or notto reuse a configuration which was used during last time the UE was inRRC_CONNECTED. The indication is transmitted by a network node, such aseNB. The UE could use or apply the configuration upon receiving theindication. The configuration could be the configuration of the UEduring the last or previous time when the UE was in RRC_CONNECTED.Furthermore, the configuration was not included in an RRCConnectionSetupmessage. In one embodiment, the indication could be included in anRRCConnectionSetup message. Alternatively, the indication could beincluded in an RRCConnectionReconfiguration message.

FIG. 8 is a flow chart 800 in accordance with an exemplary embodiment.In step 805 of FIG. 8, an indication is used to tell a UE to keep orretain a configuration which is currently used after entering RRC_IDLE.The indication is transmitted by a network node, such as eNB. After theUE receives the indication, the UE retains and does not release ordiscard the configuration upon leaving RRC_CONNECTED. However, theconfiguration may be released or discarded in at least one of thefollowing conditions: (i) when a RRC connection re-establishmentprocedure is initiated or completed, (ii) when the UE connects to a cellor eNB or TA or RAT which is different from the cell or eNB or TA or RATwhere the indication was received, or (iii) when the UE changes S-TMSI.In one embodiment, the indication could be included in anRRCConnectionSetup message. Alternatively, the indication could beincluded in an RRCConnectionReconfiguration message or anRRCConnectionRelease message.

FIG. 9 is a flow chart 900 in accordance with an exemplary embodiment.In step 905 of FIG. 9, a UE could send an indication to indicate theUE's preference of using a configuration that was used during last timethe UE was in RRC_CONNECTED. The indication is received by a networknode, such as eNB. The UE stores the configuration which was used duringlast time the UE was in RRC_CONNECTED. In other words, the storedconfiguration could be the configuration of the UE during the last timethe UE was in RRC_CONNECTED. In one embodiment, the indication could beincluded in an RRCConnectionRequest message. Alternatively, theindication could be included in an RRCConnectionSetupComplete message.In addition, the location of the UE may be the same as the location lasttime the UE in RRC_CONNECTED. Furthermore, the UE may connect to an eNBor cell which is the same eNB or cell that the UE connected to the UEduring the last time the UE was in RRC_CONNECTED. Also, the UE may enterRRC_CONNECTED triggered by an application(s) which is the sameapplication(s) as last time triggering the UE entering RRC_CONNECTED.

In one embodiment, the configuration can include at least one of thefollowing: (i) a security configuration, such as security key, KeNB,ciphering algorithm, or integrity protection algorithm, (ii) ameasurement configuration, or (iii) a radio resource configuration, suchas radio bearer configuration for SRB or DRB, MAC configuration, orphysical channel configuration.

Referring back to FIGS. 3 and 4, in one embodiment, the device 300implements a network node (such as eNB) and includes a program code 312stored in memory 310. In one embodiment, the CPU 308 could execute theprogram code 312 to transmit a first indication to a UE to tell the UEto remember a configuration which is currently used after the UE entersRRC_IDLE. The CPU 308 could also execute the program 312 to transmit asecond indication to a UE to tell the UE to use a configuration whichwas used during the last time the UE was in RRC_CONNECTED. The CPU 308could further execute the program 312 to receive a third indication fromthe UE to indicate that the UE wants to use the configuration which wasused during the last time the UE was in RRC_CONNECTED. In addition, theCPU 308 can execute the program code 312 to perform all of theabove-described actions and steps or others described herein.

Referring back to FIGS. 3 and 4, in an alternative embodiment, thedevice 300 implements a UE and includes a program code 312 stored inmemory 310. In one embodiment, the CPU 308 could execute the programcode 312 (i) to receive a first indication from the network node to tellthe UE to remember a configuration which is currently used after the UEenters RRC_IDLE, and (ii) to retain and not release or discard theconfiguration upon leaving RRC_CONNECTED. The CPU 308 could furtherexecute the program code 312 to receive a second indication from thenetwork node to tell the UE to use the configuration which was usedduring the last time the UE was in RRC_CONNECTED. The CPU 308 could alsoexecute the program code 312 to transmit a third indication to thenetwork node to indicate that the UE wants to use the configurationwhich was used during the last time the UE was in RRC_CONNECTED. Inaddition, the CPU 308 can execute the program code 312 to perform all ofthe above-described actions and steps or others described herein.

Various aspects of the disclosure have been described above. It shouldbe apparent that the teachings herein may be embodied in a wide varietyof forms and that any specific structure, function, or both beingdisclosed herein is merely representative. Based on the teachings hereinone skilled in the art should appreciate that an aspect disclosed hereinmay be implemented independently of any other aspects and that two ormore of these aspects may be combined in various ways. For example, anapparatus may be implemented or a method may be practiced using anynumber of the aspects set forth herein. In addition, such an apparatusmay be implemented or such a method may be practiced using otherstructure, functionality, or structure and functionality in addition toor other than one or more of the aspects set forth herein. As an exampleof some of the above concepts, in some aspects concurrent channels maybe established based on pulse repetition frequencies. In some aspectsconcurrent channels may be established based on pulse position oroffsets. In some aspects concurrent channels may be established based ontime hopping sequences. In some aspects concurrent channels may beestablished based on pulse repetition frequencies, pulse positions oroffsets, and time hopping sequences.

Those of skill in the art would understand that information and signalsmay be represented using any of a variety of different technologies andtechniques. For example, data, instructions, commands, information,signals, bits, symbols, and chips that may be referenced throughout theabove description may be represented by voltages, currents,electromagnetic waves, magnetic fields or particles, optical fields orparticles, or any combination thereof.

Those of skill would further appreciate that the various illustrativelogical blocks, modules, processors, means, circuits, and algorithmsteps described in connection with the aspects disclosed herein may beimplemented as electronic hardware (e.g., a digital implementation, ananalog implementation, or a combination of the two, which may bedesigned using source coding or some other technique), various forms ofprogram or design code incorporating instructions (which may be referredto herein, for convenience, as “software” or a “software module”), orcombinations of both. To clearly illustrate this interchangeability ofhardware and software, various illustrative components, blocks, modules,circuits, and steps have been described above generally in terms oftheir functionality. Whether such functionality is implemented ashardware or software depends upon the particular application and designconstraints imposed on the overall system. Skilled artisans mayimplement the described functionality in varying ways for eachparticular application, but such implementation decisions should not beinterpreted as causing a departure from the scope of the presentdisclosure.

In addition, the various illustrative logical blocks, modules, andcircuits described in connection with the aspects disclosed herein maybe implemented within or performed by an integrated circuit (“IC”), anaccess terminal, or an access point. The IC may comprise a generalpurpose processor, a digital signal processor (DSP), an applicationspecific integrated circuit (ASIC), a field programmable gate array(FPGA) or other programmable logic device, discrete gate or transistorlogic, discrete hardware components, electrical components, opticalcomponents, mechanical components, or any combination thereof designedto perform the functions described herein, and may execute codes orinstructions that reside within the IC, outside of the IC, or both. Ageneral purpose processor may be a microprocessor, but in thealternative, the processor may be any conventional processor,controller, microcontroller, or state machine. A processor may also beimplemented as a combination of computing devices, e.g., a combinationof a DSP and a microprocessor, a plurality of microprocessors, one ormore microprocessors in conjunction with a DSP core, or any other suchconfiguration.

It is understood that any specific order or hierarchy of steps in anydisclosed process is an example of a sample approach. Based upon designpreferences, it is understood that the specific order or hierarchy ofsteps in the processes may be rearranged while remaining within thescope of the present disclosure. The accompanying method claims presentelements of the various steps in a sample order, and are not meant to belimited to the specific order or hierarchy presented.

The steps of a method or algorithm described in connection with theaspects disclosed herein may be embodied directly in hardware, in asoftware module executed by a processor, or in a combination of the two.A software module (e.g., including executable instructions and relateddata) and other data may reside in a data memory such as RAM memory,flash memory, ROM memory, EPROM memory, EEPROM memory, registers, a harddisk, a removable disk, a CD-ROM, or any other form of computer-readablestorage medium known in the art. A sample storage medium may be coupledto a machine such as, for example, a computer/processor (which may bereferred to herein, for convenience, as a “processor”) such theprocessor can read information (e.g., code) from and write informationto the storage medium. A sample storage medium may be integral to theprocessor. The processor and the storage medium may reside in an ASIC.The ASIC may reside in user equipment. In the alternative, the processorand the storage medium may reside as discrete components in userequipment. Moreover, in some aspects any suitable computer-programproduct may comprise a computer-readable medium comprising codesrelating to one or more of the aspects of the disclosure. In someaspects a computer program product may comprise packaging materials.

While the invention has been described in connection with variousaspects, it will be understood that the invention is capable of furthermodifications. This application is intended to cover any variations,uses or adaptation of the invention following, in general, theprinciples of the invention, and including such departures from thepresent disclosure as come within the known and customary practicewithin the art to which the invention pertains.

What is claimed is:
 1. A method implemented in a UE (User Equipment),comprising: receiving a first indication from a network node to tell theUE to remember, after the UE enters RRC_IDLE, a first configurationwhich is currently used while the UE is in RRC_CONNECTED; keeping thefirst configuration upon leaving RRC_CONNECTED; and releasing the firstconfiguration when the UE connects to a Radio Access Technology (RAT)different from where the first indication was received.
 2. The method ofclaim 1, wherein the first indication is at least included in anRRCConnectionSetup message.
 3. The method of claim 1, wherein the firstindication is at least included in an RRCConnectionReconfigurationmessage.
 4. The method of claim 1, wherein the first indication is atleast included in an RRCConnectionRelease message.
 5. The method ofclaim 1, further comprises: releasing the first configuration at leastwhen a Radio Resource Control (RRC) connection re-establishmentprocedure is initiated or completed.
 6. The method of claim 1, furthercomprises: releasing the first configuration at least when the UEconnects to a cell, evolved Node B (eNB), or Tracking Area (TA) which isdifferent from where the first indication was received.
 7. The method ofclaim 1, further comprises: releasing the first configuration at leastwhen the UE changes System Architecture Evolution Temporary MobileStation Identifier (S-TMSI).
 8. The method of claim 1, wherein the firstconfiguration includes at least a security configuration.
 9. The methodof claim 1, wherein the first configuration includes at least ameasurement configuration.
 10. The method of claim 1, wherein the firstconfiguration includes at least a radio resource configuration.
 11. A UE(User Equipment) in a wireless communications system, the UE comprising:a control circuit for realizing functions of the UE; a centralprocessing unit coupled to the control circuit for executing a programcode to operate the control circuit; and a memory coupled to the centralprocessing unit for storing the program code; wherein the program codecomprises: receiving a first indication from a network node to tell theUE to remember, after the UE enters RRC_IDLE, a first configurationwhich is currently used while the UE is in RRC_CONNECTED; keeping thefirst configuration upon leaving RRC_CONNECTED; and releasing the firstconfiguration when the UE connects to a Radio Access Technology (RAT)different from where the first indication was received.
 12. The UE ofclaim 11, further comprises: releasing the first configuration at leastwhen a Radio Resource Control (RRC) connection re-establishmentprocedure is initiated or completed.
 13. The UE of claim 11, furthercomprises: releasing the first configuration at least when the UEconnects to a cell, evolved Node B (eNB), or Tracking Area (TA) which isdifferent from where the first indication was received.
 14. The UE ofclaim 11, further comprises: releasing the first configuration at leastwhen the UE changes System Architecture Evolution Temporary MobileStation Identifier (S-TMSI).
 15. The UE of claim 11, wherein the firstconfiguration includes at least a security configuration.
 16. The UE ofclaim 11, wherein the first configuration includes at least ameasurement configuration.
 17. The UE of claim 11, wherein the firstconfiguration includes at least a radio resource configuration.
 18. TheUE of claim 11, wherein the first indication is at least included in anRRCConnectionSetup message.
 19. The UE of claim 11, wherein the firstindication is at least included in an RRCConnectionReconfigurationmessage.
 20. The UE of claim 11, wherein the first indication is atleast included in an RRCConnectionRelease message.